The invention relates to strategies for managing the energy sources involved in powering (combustion/electric) hybrid vehicles.
More particularly, it relates to an energy management method for a hybrid vehicle drive system, the purpose of which is to minimize fuel consumption and preserve the useful life of the electrical energy storage means.
A hybrid drive system is schematically illustrated in FIG. 1.
Such a drive system typically comprises a heat engine 1 supplying mechanical energy to the vehicle drive wheels 2 (just one wheel is shown), one or more electric machines 3 (just one electric machine is shown) supplying electrical energy to the vehicle wheels 2, means for storing electrical energy 4, means 5 for transmitting mechanical and electrical energy to the vehicle wheels 2, and electrical energy recovery means 7 shown enclosed by a dashed line.
One of the possible energy recovery means, also described as “natural”, is for example to use the electric machine as a current generator during deceleration. Operating as a generator, the electric machine transforms the mechanical/kinetic energy from the wheels into electrical energy.
Control of a hybrid vehicle drive system as described above is known, in particular from document EP0759370, and this control comprises selection of the drive mode (combustion/electric) according to the efficiency of the electric drive mode.
According to this document, two values of a physical quantity are compared in order to select the drive mode so as to optimize fuel consumption. Therefore, the fuel consumption must be known continually.
In this document, the fuel consumption of the heat engine is calculated from the average efficiency of the heat engine, which is determined empirically from a driving history.
Using the engine efficiency to calculate the fuel consumption of the heat engine yields imprecise results, since the efficiency value includes losses related to engine speed.